Abstract: Aluminum based composite materials have been widely used for its excellent physical and mechanical properties. RE/Al₂O₃ nano powders were added into 2219-O aluminum alloy and the composite materials were prepared by friction stir processing. Meanwhile, the microstructure and properties of the specimen were analyzed and tested by using metallographic, tensile, hardness, SEM, EDS and XRD methods. The results show that, the stir zone metal occurs obviously plastic deformation and continuous dynamic recrystallization under strong friction stir. Besides, fine equiaxed grain and onion rings structure are found in the stir zone. The tensile strength of the composite material can reach 163% and yield strength can reach 195% of matrix ones. Meanwhile, the hardness of the composite material obviously increases, but the rare earth content has little influences on the microstructure and mechanical properties of matrix composites. The key issue to prepare the composite material is how to control the powder addition and tunnel defects.